1. Field of the Invention
The invention relates generally to rosin-based synthetic resins suitable for use in printing inks and to processes for their production. Particularly, the invention relates to rosin-dicyclopentadiene resins and lithographic ink formulations incorporating said resins.
2. Description of the Prior Art
To produce lithographic inks, two major types of ink resins are employed, rosin-based resins and hydrocarbon resins. The basic hydrocarbon resins are produced from either thermal polymerization of reactive olefins composed chiefly of dicyclopentadiene or Lewis acid catalyzed polymerization of various vinyl aromatic monomers.
Dicyclopentadiene (DCPD) is a material which will readily form hydrocarbon resins When heated to temperatures greater than 200.degree. C. Polymerization apparently occurs through cyclopentadiene which is formed when dicyclopentadiene is heated above 170.degree. C. Chain growth of the polymer proceeds via a free radical mechanism with both 1:4 and 1:2 addition occurring as is shown in Equation I below. ##STR1##
If dicyclopentadiene is heated to 200.degree. C. and held there, the predominant reaction occurring is oligomerization by the Diels-Alder addition of cyclopentadiene to the norbornyl double bond of the dimer, trimer, etc., as set forth in Equation II below. ##STR2##
Usually, the largest oligomer formed is the pentamer. The Diels-Alder oligomers are often referred to as thermal polymer of dicyclopentadiene, but their low molecular weight and insolubility in organic solvents make them useless for commercial ink applications.
The reaction of rosin and tall oil with dicyclopentadiene under pressure at temperatures greater than 400.degree. F. (204.degree. C.) is known to produce a resinous material. The resins produced, claimed useful as synthetic surface coatings, particularly in the paint and varnish field, are light colored resins with low softening points and reduced acid numbers. The softening points of such resins made with rosin are in the range of 215.degree.-250.degree. F. (102.degree.-121.degree. C.). The resin products made from refined tall oil are liquids unless a substantial excess of cyclopentadiene is employed.
Cyclopentadiene can be used for the reaction with rosin and tall oil. However, as cyclopentadiene quickly equilibrates with dicyclopentadiene under the above conditions, the use of dicyclopentadiene produces similar products.
The drop in acid number of such products indicates the consumption of the acid function of the rosin or tall oil. This results from the addition of carboxylic acid functions across double bonds to produce esters. In the presence of dicyclopentadiene, it is assumed that this addition occurs across the norbornyl-type double bonds of DCPD, DCPD oligomers, and DCPD polymers, as set forth in Equation III, below. ##STR3##
Likewise, the thermal polymerization of dicyclopentadiene with tall oil fatty acids is attributed, in U.S. Pat. No. 4,292,221, to the addition of the acid functions to the bicycloheptene double bonds of the hydrocarbon resin. The patentees teach fatty acid heated with dicyclopentadiene to produce resins suitable for offset printing.
In U.S. Pat. No. 4,242,244, carboxylic acids are taught to add to preformed thermal cyclopentadiene resins if the resins contain the reactive bicycloheptene double bonds, as set forth in Equation IV below. ##STR4##
The reaction between dicyclopentadiene, a mixture of dimerized conjugated aliphatic cyclic and non-cyclic dienes of five carbon atoms, and distilled tall oil is described in U.S. Pat. No. 4,056,498 to produce an intermediate which is adducted with maleic anhydride to produce a final ink resin.
Printing ink resins are disclosed in U.S. Pat. No. 4,189,410 to be prepared by reacting dicyclopentadiene, rosin acids, and a hydrocarbon containing material selected from debutanized aromatic concentrates, C.sub.5 -olefins, and acyclic, conjugated C.sub.5 -dienes; and, in U.S. Pat. No. 4,433,100, printing ink resins are prepared by reacting dicyclopentadiene, rosin acids, and a hydrocarbon selected from mono-olefins, diolefins, and polyenes having more than five carbon atoms and no aromatic rings. In U.S. Pat. No. 4,474,057, printing ink resins are prepared by reacting dicyclopentadiene, tall oil or rosin acids, an ethylenically unsaturated lower aliphatic acid or anhydride, a material with two reactive groups including a hydroxyl group, and a hydrocarbon. The hydrocarbon can be that disclosed in U.S. Pat. Nos. 4,189,410 or 4,433,100, or it can be a dimerized aliphatic, cyclic, or non-cyclic diene of five carbon atoms.
Also, rosin-cyclopentadiene resins are disclosed for gravure printing in U.S. Pat. No. 4,092,283. A cyclopentadiene resin is heated with rosin and maleic anhydride to 250.degree.-270.degree. C. to form ester bonds, obtaining resins having an acid number of 60 and a softening point of 165.degree. C. After several hours, metal oxides are added to form resinates.
It was found, however, that when rosin and dicyclopentadiene were thermally reacted, low acid number hybrid resins were obtained. Their major shortcoming was low Gardner viscosities relative to standard rosin-based or reactive hydrocarbon lithographic ink resins. In order to have a viable new resin for the lithographic ink market, hybrid resins with higher viscosities are needed.
It is an object of the present invention to provide a novel rosin-based resin suitable for use in printing inks.
A further object of the present invention is to provide a rosin-based resin having viscosity and solubility properties which enable its incorporation in lithographic inks.